Sticking a tree in a pot/box significantly larger than it was in before will not get you the results your looking for. The soil will stay too wet and the trees' roots could rot. Instead you you should scale up the pot every year during the heat of the summer. Ficus too little being a dwarf is also slower growing compared to a regular Benjamin ficus. Tropicals do benefit from a domarcy also- so you'll do better by giving them some rest. By doing so you'll be rewarded with more growth in the summer. In the winter I trim them heavly and cut all med & large leaves in half. This helps build ramification and the openess discourages scale and other pests. I also stop fertilizing from nov thru march.
See
http://www.bonsaihunk.8m.com/ , Jerry has some articles on light and is a top source for indoor growing info. You'll see in one of the articles the difference between a flourescent & a MH bulb. I upgraded to MH 4 years ago and would never go back.